The Role of VC Precipitates in Hydrogen Assisted Cracking of Vanadium Modified 2⅟₄Cr1Mo Steel

Author(s)

Kevin Nibur, Sylvain Pillot, Brian Somerday, Richard P. Gangloff

On-Site Speaker (Planned)

Kevin Nibur

Abstract Scope

The resistance of bainitic 2⅟₄Cr1MoV plate and weld metal to internal hydrogen assisted cracking (IHAC) has been evaluated between 25oC and 150oC using precracked specimens thermally precharged with 7-9wppm hydrogen. Elastic-plastic crack initiation threshold and stable growth resistance were measured using slow rising crack mouth opening displacement and direct current potential drop crack detection. These measures of IHAC are only modestly reduced from those of non-charged specimens; for example, the threshold is above 100 MPa√m for all combinations of variables. A beneficial role of nano-scale VC precipitates is suggested because IHAC fracture thresholds of 2⅟₄Cr1Mo, without vanadium, are consistently in the range of 20-40 MPa√m. Additional experiments utilizing non-charged specimens stressed in pressurized hydrogen gas are compared with the IHAC results to elucidate the role of VC precipitates as beneficial hydrogen trap sites. These data enable a quantitative assessment of the minimum pressurizing temperature of heavy-wall petrochemical reactors to avoid IHAC.